A survey within the medical community revealed that an instrument capable of continuously and accurately monitoring temperature at multiple locations in and around a tumor during hyperthermia therapy is needed. The treatment of cancer by hyperthermia is a process by which elevated temperatures are used to destroy cancer cells. Since the application of elevated temperatures may also damage healthy tissue, a means must be provided to selectively apply the heat and monitor the temperature in and around the tumor being treated. OPTECH's sensor provides the following features. o Potential for an array of up to five temperature sensors along a single optical fiber, o small size (0.5 mm in diameter and 1.0 mm long per sensor), o resolution of 0.01 C and an accuracy of +/- 0.1 C, o reliable and safe (nonthrombogenic) and, o dielectric sensors, therefore, measurements can be made in a microwave environment. The specific aim of this Phase I proposal is to build a prototype temperature sensor having two spacially separated temperature sensitive regions on a single optical fiber and to validate its predicted performance under laboratory conditions. The individual sensors can be separately interrogated. The technique will be extended during Phase II to include up to five sensors on one fiber.